Surface-mountable (SMD) light-emitting diode components (LEDs) in leadframe technology are often mounted in a transfer-moulded or injection-moulded plastic package body prefabricated on the leadframe, are connected there to electrical leads and, for protection against harmful external influences, are encapsulated with a transparent casting compound, through which light is coupled out during the operation of the LEDs.
In particular in the case of so-called conversion LEDs, in which at least part of the radiation emitted by the semiconductor chip (hereafter primary radiation) is converted by a luminescent material in the casting compound into radiation with an at least partly changed wavelength in comparison with the primary radiation, it is technically often difficult to introduce the intended amount of luminescent material at the intended location. Difficulties are caused in particular by a distribution of the wavelength and a distribution of the brightness of semiconductor chips that are nominally identical. Among the technical problems that are often observed are segregation effects of the luminescent material after application of the casting compound to the chip. The aforementioned aspects make a significant contribution to non-uniformities in the radiation characteristic of conventional conversion LEDs and adversely affect the yield in mass production.
Known conversion LEDs are described for example in the documents WO 97/50132 A1, WO 98/12757 A1 and WO 01/50540 A1.